The intent of the proposed project is to characterize human acute leukemia-associated antigens in individual patients. A new technique will be used to prepare heteroantisera specific for leukemic antigens in mice previously rendered tolerant with cyclophosphamide to normal leukocyte antigens of the same patient. It is anticipated that cross-reactivity and cross-absorption studies using these antisera will yield important information regarding the relationship between neoantigens expressed on different types of leukemia, between leukemia-associated antigens and those of other human and animal tumors, and embryonic cells. These data should bear importantly on the future prospects of immunotherapy of leukemia, production of leukemic vaccines, and diagnosis of leukemia remissions.